1. Field
This invention generally relates to wireless communications technology and, more particularly, to systems and methods for using a common baseband processor to enable communications with multiple bandwidths.
2. Background
Frequency spectrum is increasing becoming a scarce commodity as a greater number of communications systems proliferate. Thus, there is increasing pressure to use unlicensed frequency bands. Simultaneously, there is pressure upon communication device manufactures to supply devices that operate in different frequency bands, using different communication protocols. Communication protocols of emerging interest are those compliant with IEEE 802.11g, 802.11a, IEEE 802.11n, and ultra-wideband (UWB). The UWB protocols are described in the Ecma-368 High Rate Ultra Wideband PHY and MAC standard.
Generally, the Federal Communications Commission (FCC) defines UWB as a system using a bandwidth that exceeds the lesser of 500 megahertz (MHz), or 20% of the center frequency. The FCC uses −10 dB emission points to determine bandwidth, and to define the center frequency. UWB technology may be applicable to high and low data rate personal area networks (PANs). The advantage of the large bandwidth is that the system should be able to deliver high date rates over short distances, while sharing the spectrum with other communications systems. For this reason, the FCC has authorized the unlicensed use of UWB in the band between 3.1 gigahertz (GHz) and 10.6 GHz.
UWB can be generated as a pulse type system, where each transmitted pulse occupies the entire UWB frequency bandwidth. An aggregation of narrowband subcarriers are used to generate at least 500 MHz of frequency bandwidth. For example, an orthogonal frequency division multiplexing (OFDM) system may be used. OFDM splits the digital information to be transmitted over a plurality of parallel slower data rate streams. Each of the parallel data streams is modulated onto a particular subcarrier, using a technique such a quadrature phase shift keying (QPSK) for example, and transmitted at a relatively low data rate. The subcarrier frequency is chosen to minimize crosstalk between adjacent channels, which is referred to as orthogonality. The relatively long symbol duration helps minimize the effects of multipath, which is the degradation caused by signals arriving at different times.
802.11, often referred to as WiFi, describes a group of standards that use the same protocol, but different modulation techniques. At the time of this writing, Draft 2.0 of the Working Group is guiding the development of 802.11n. 802.11n operates in the Industrial, Scientific, and Medical (ISM) band at a center frequency of either 2.4 or 5.7 GHz, or in the National Information Infrastructure (U-NII) band (5.2 GHz), at a typical data rate of between 200 and 540 megabits per second. 802.11n builds upon previous 802.11 standards by adding a multi-antenna system referred to as multiple-input multiple-output (MIMO). Each antenna is associated with a separate transmitter and receiver for processing independent, parallel channels. MIMO permits an increase in throughput, without increasing the overall system frequency bandwidth or transmitter power.
802.11n, when using the 2.4 GHz band North American channelization scheme, divides the 2.4 GHz spectrum into 11 overlapping, staggered channels whose center frequencies are 5 megahertz (MHz) apart. A 20 MHZ channel is divided into 56 subcarriers, with a subcarrier spacing of 0.3125 MHz, or 40 MHz channels with 112 subcarriers. Note: some subcarriers are used as pilot subcarriers. Like the above-described UWB system, 802.11n uses OFDM to transmit subcarriers.
It would be advantageous if a communications device could be made to operate in accordance with different protocols, using the same baseband processor equipment. For example, it would be advantageous if a communications device could be made to operate in accordance with both the UWB and 802.11 standards using a shared baseband processor.